In general, an air for combustion to be supplied into an engine of an outboard motor contains therein water. When the water contained in the air for combustion is introduced into the engine, an output is lowered and a fuel consumption is deteriorated. In order to prevent the water contained in the air for combustion from entering into the engine, there is an intake apparatus configured to introduce the air for combustion through a space between an engine cover and the engine (for example, refer to Patent Document 1: Japanese Patent Application Publication No. 2007-8416A and Patent Document 2: Japanese Patent Application Publication No. 2008-88881A). According to the intake apparatus disclosed in Patent Documents 1 and 2, an intake air path from an intake introduction port of the engine cover to a combustion chamber is sufficiently secured to prevent the entry of water into the engine.
However, according the intake apparatus disclosed in Patent Documents 1 and 2, it is necessary to provide a sufficient space between the engine cover and the engine so as to secure the intake air path. As a result, the outboard motor is enlarged.
In addition, according to the intake apparatus disclosed in Patent Documents 1 and 2, the air for combustion introduced in the engine cover is delivered to an engine room. Then, the air for combustion flows in a space in the vicinity of an engine accommodated in the engine room and is then delivered to the combustion chamber. Thus, the air for combustion introduced into the engine cover is warmed up during the flowing in the vicinity of the engine. For this reason, the output is lowered and the fuel consumption is deteriorated.
Therefore, in order to improve the fuel consumption of the outboard motor, an intake apparatus is considered which is configured to couple the intake introduction port of the engine cover and a throttle body by an intake duct so as to directly introduce the air for combustion without through the engine cover. According to this intake apparatus, since the intake can be made without warming up the air for combustion, it is possible to improve the output and the fuel consumption. However, according to this intake apparatus, a noise occurs upon the intake and the water contained in the air for combustion can easily enter into the engine.
Hence, in order to prevent the noise upon the intake and the entry of water into the engine, the intake apparatus configured to directly introduce the air for combustion is provided with an intake silencer box (an air cleaner device) that is attached in an air passage (for example, refer to Patent Document 3: Japanese Patent Application Publication No. 2007-291982A). The intake silencer box disclosed in Patent Document 3 has a box shape comprised of a main body part and a cover part, and an air filter element is provided in the box. The main body part is provided with an inlet of the air for combustion and the cover part is provided with an outlet of the air for combustion. Also, an intake duct is coupled to the outlet of the air for combustion provided for the cover part. The water contained in the air for combustion is captured by the intake silencer box. Thereby, the entry of water into the engine is prevented.
However, according to the intake silencer box disclosed in Patent Document 3, it is necessary to detach the cover part from the main body part and the cover part from the intake duct when checking an interior of the intake silencer box. For this reason, a maintenance characteristic of the intake silencer box is poor.
In addition, according the intake silencer box disclosed in Patent Document 3, since the air for combustion introduced into the intake silencer box directly passes through the air filter element, most of the water contained in the air for combustion is captured by the air filter element. For this reason, the lifetime of the air filter element is shortened, so that a replacement frequency of the air filter element is increased.